Electrode furnace



Sept. 20, 1960 A. F. HOLDEN ELECTRODE FURNACE Filed sept. 2o, 1957 5Sheets-Sheet 1 INVENTOR.

ARTfM/s /VOL f/V BY M, a/ M ATTORNEYS Sept. 20, 1960 A. F. HOLDEN2,953,614

ELECTRODE FURNACE Filed Sept. 20, 1957 5 Sheets-Sheet 2 Sept. 20, 1960 vA. F. HOLDEN 2,953,614

ELECTRODE FURNACE Filed Sept. 20, 1957 5 Sheets-Sheet I5 INVENTOR.

ARTI/MAJ f.' A/0 yf/v ATTOR/V'KS Sept. 20, 1960 A. F. HQLDEN ELECTRODEFURNACE 5 Sheets-Sheet 5 Filed Sept. 20, 1957 INVENTOR.

Afri/nn: F. //o of BY 17, 441.@ 4.7

2,953,614 Patented Sept. 20, 1960 ELECTRODE FURNACE Artemas F. Holden,2195 S. Milford, R.R. 1, Milford, Mich.

Filed Sept. 20, 1957, Ser. No. 685,161

11 Claims. (Cl. 13-23) This invention pertains to an electrode furnacewherein each electrode may have either or both its hot leg portion andits cold leg portion embedded in a refractory material with spacedlateral projections providing spaced supports thereto. The projectionsmay have an exposed end surface for electrical conduction. In anelectric salt bath furnace wherein the electrodes are subject to wear,it has been found advantageous to hang the electrodes over the furnacewall so that they may be easily removed and replaced. It is alsodesirable to cover completely the molten bath in order to minimize heatand vapor loss to the atmosphere from the top of the bath. In the past,it has been found diiiicult to provide a completely covered bath and, atthe same time, permit a removable electrode construction because thespaces between electrodes, between electrodes and the furnace cover, andbetween electrodes and the furnace wall could not readily be sealed orcompletely covered.

This invention provides for embedding the supporting portion of eachelectrode assembly in a monolithic refractory material or casting andfor utilizing such casting asa segment of the furnace cover which, withother similar castings, form a substantially completely covered furnacearea while still permitting individual electrode removal.

In a preferred embodiment described below, the refractory material Aiscovered with a metal top. A horizontal row of castings is placed on afurnace wall. Hinged tothe metal top is an access cover which may bepivoted about the hinges to provide an opening for work insertion intothe bath. The supporting or horizontal cold leg portion of the electrodeassembly extends beyond the Casting outside the furnace for connectionto vertical power cables which extend downwardly to a power source. Anyelectrode may be quickly and individually removed by simply removingfirst the hinge pin, the metal top, then sliding the casting outwardlyuntil the electrodes contact the furnace wall, tilting the casting aboutthe furnace Wall, and then lifting the casting in the direction of thetilt angle.

This linvention also provides for replaceable electrode connectedprojections of relatively small size and inexpensive nature, whichprojections are fixed to the electrode at spaced intervals and areembedded in a refractory material which substantially isolates theelectrodes from the salt bath and which cooperates with the conductingportions to support the electrode at spaced intervals along its lengthwhich at high temperatures prevents deformation of the electrode. Byisolating the electrodes from the salt bath, the electrodes areprotected from any corrosive action from the bath or products thereof atthe air bath interface or in the bath itself.

In an electric salt bath furnace, the conduction through a salt bathbetween electrodes is used to bring the bath up to temperature andmaintain it there. Especially in deep baths, where the electrodes arenecessarily longer to provide for even bath temperature, during highbath temperatures the electrode weight tends to stretch and weaken itsintermediate or upper portions. When this deformation takes place, theelectrodes usually have to be replaced.

A second cause for frequent electrode replacement localized wearing awayof a portion of the electrode. One worn spot on the electrode willrequire its complete replacement. With this invention, these costlyreplacements are largely avoided. This invention provides forprojections or stubs which are fixed to each electrode at spacedintervals and further provides for the embedding of the stub-electrodecombination in a refractory material. The refractory casting may exposeone surface of the conductive stubs to the furnace bath. Stubs connectedto electrodes of opposite polarity then co-operate to establish acurrent through the salt bath which provides for the temperaturerequirement. With this construction, the electrodes per se are notexposed directly to the salt bath and they are supported by the stubs atintervals along their length. This prevents localized wear of theelectrodes and sagging and stretching at high temperatures. When thestubs become worn or defective, the refractory casting may be removedfrom the furnace and the stubs burned out or otherwise removed andreplaced. This provides a considerable cost saving since only the Wornstub need be replaced and each stub, of course, costs but a smallfraction of an electrode. The portion of the bath in conventionalfurnaces which surrounds the electrodes is unusable since contactbetween the workpiece and electrode is undesirable. This means thatpower is required to heat a portion of the bath that is never used. Withthis invention, this unused portion is virtually eliminated and byrecessing each stub in the refractory material, contact with theworkpiece is prevented.

If desired, before casting the refractory material, the stubs may bewrapped in a combustible material which when heated will decomposeleaving a small clearance between the stubs and the hardened refractorymaterial. This clearance is provided to accommodate any difference inco-eilcients of expansion of the electrode and the refractory material.

In addition to increased electrode life, this invention makes feasibleelectrode length not before practical. A limit had been imposed upon thelength of Ian electrode due to the fact that its own weight would, at ahigh temperature, cause stretching and deformation. With this invention,any length electrode, and hence any depth of salt bath furnace, may beused since the electrode is supported at spaced intervals. In thisconnection, an embodiment of this invention is shown having pinsattached to each electrode and embedded in the refractory. These pinsare not exposed to the 'salt bath and are used for electrode supportonly. A lower portion of the electrode is exposed to the bath forheating purposes.

It is, therefore, an object of this invention to provide an electricsalt bath furnace that may be completely covered and has electrodes withexternal projections` which support the electrodes along its length andwhich may have exposed end portions for electric conduction. It isanother object to provide a furnace that has individually removableelectrodes. It is another object to provide a furnace that has a minimumheat loss due to radiation and has easily replaceable electrodes. It isan object to provide an electrode assembly having a vertical downwardlydepending electrode for immersion in a salt bath and a horizontally,outwardly extending cold leg portion which extends over the furnace wallembedded in a refractory material. It is another object to haveanchoring bars or pins transverse to said cold leg portion for rigid andsecure holding in said refractory. It is a further object to provide afurnace construction having a series of refractory elements positionedside by side along a furnace wall to form a substantially complete covertothe atmosphere. It is another object to combine with this constructiona furnace access cover.

A further object is to provide the bath or hot leg of the electrode withlateral projections and then embed this leg in a refractory casting.Another object is to provide each of the lateral projections with anopen exposed end so that electrical conduction may occur between theprojections of opposite electrodes. Another object is to isolate thebath or hot leg portions from the salt bath thereby preventing localizedwear due to corrosion or conduction. A further object is to support eachelectrode at spaced intervals along its length to prevent electrodedeformation. It is an object to provide a lead bath along the floor ofthe furnace to retain and suspend bath impurities for easy removal.A'further object is -to provide an additive in the lead bath which willhelp precipitate the sludge and foreign matter.

These and other objects and advantages will become more apparent when apreferred embodiment is described in connection with the drawings inwhich:

Figure 1 is a sectioned view of a furnace having the cold and hot legsof the electrode embedded in a refractory material and having a leadbath along its bottom;

Fig. 2 is a view taken at 2-2 of Figure 1;

Figure 3 is a plan view of a furnace having the cold legs embedded inrefractory material;

Figure 4 is a section taken at 4-4 of Figure 3;

Figure 5 is a perspective view of an electrode assembly of thisinvention with cast concrete shown in phantom around the cold legportion;

Figure 6 is a plan view of a salt bath furnace having four electrodeswith each electrode having stub portions exposed to the salt bath;

Figure 7 is a section taken at 7-7 of Figure 6 showing the exposed stubsurfaces and also sectioned stubs;

Figure 8 is a section taken at 8 8 of Figure 7;

Figure 9 is a partial cutaway view of a furnace having a secondembodiment of this invention wherein the electrode supports are notexposed to the bath;

Figure l0 is an enlarged section taken at lO-10 of Figure 9 showing theclearance about each supporting pin which allows for expansion andcontraction;

Fig. 11 is a section taken at 11--11 of Figure 9; and

Figure 12 is a view of a recessed stub.

In Figure l is shown an embodiment of this invention wherein furnace 9has wall 12 which supports a refractory casting 13 which has embeddedtherein electrode 14 with cold leg 15 and hot leg 16. As shown, hot leg16 has laterally projecting stubs 17 having ends exposed to the saltbath 18 and electrical current flow takes place between exposed stubends of electrodes of opposite polarity. In the embodiment shown inFigure 1, each electrode is cast in refractory material 13 and they areplaced either side by side or between furnace wall extensions so as toprovide a continuous wall along the top of the furnace. Plate 19 is thenplaced over this continuous wall to which cover 2Q is pivoted to form acompletely enclosed electrode furnace. In Figure 2 is shown a view takenat 2-2 of Figure l and the lower portion of refractory casting 13 inwhich stubs 17 can be seen. Also shown in Figure 1 is pan 10 along thebottom of furnace 9 which contains a lead bath 11 which is positioned toreceive the sediment and sludge which would otherwise accumulate on thefurnace floor and present a difficult removal problem. It may bedesirable, especially in a neutral bath, to leave the pan dry to receivethe sediment and waste. There may be a clearance of one-half inchbetween pan and the furnace walls and pan 10 may be two inches high andone-eighth of an inch to one-quarter of an inch in thickness whencomprised of a metal suitable to bath temperatures. Low carbon steel, ornickel alloys may be used for the pan metal. With bath 11, the sludgemay be skimmed 0E, reducing time and costs and furthering the life offurnace 9. If desired, an alloy may be added to the bath 11 which willaid in precipitating or separating the foreign matter so that it can beeasily skimmed from the top of bath 11. A copper tin phosphorous alloywith the tin between 4% and 11% and the phosphorous between .25% and.35% or a copper tin (5%) and lead (5%) alloy may be used. Use of thecopper additive is particularly advantageous when a copper or copperalloy coating on the steel is desired. Lead (67-97%) may be alloyed witheither antimony, calcium or magnesium and lead may be alloyed with tinor with tin and magnesium in an amount to produce satisfactory moltenconditions under bath temperatures when added to lead bath 11.

Two embodiments are described below, one in which the cold legs areembedded in refractory material and one in which the hot legs areembedded in refractory material.

In Figure 3 is shown furnace 21 having cast concrete blocks 22 arrangedside by side along wall 23 of the furnace. lEach block 22 has embeddedtherein the cold leg of an electrode assembly 24 which is composed of avertical electrode member 26, which is attached to two spaced horizontalcold leg steel bars 27 which are in turn connected to copper leads 28.Covers 31 are hinged at 32 to mountings on plate 33 which is placed overconcrete blocks 22. Also shown are thermocouple ports 36, sighting port37 and thermocouple 38. Pots 41 are located side by side interiorly offurnace 21.

In Figure 4 is seen more clearly the relationship between block 22,electrode assembly 24 and wall 23 of Afurnace 21. Also shown are threephantom outlines of the electrode assembly as it is removed from thefurnace. -In the irst movement for removal, the assembly and block 22are moved outwardly until the vertical electrode 26 is adjacent theinside of wall 23, as shown by the dotted line a. In the next, or b,movement, the block and electrode are tilted about an outer point ofwall 23 so that hinge 32 is cleared and then the electrode and blockassembly are lifted in tilted position from the furnace to position c.Of course, if there are hinges and a metal cover such as top 33, thenthese must first be disengaged or removed, but aside from moving theseparts, individual electrode removal is possible without disturbing otherfurnace components.

Hold-down clamps 34 tightly secure inner pots 41 to the end walls offurnace 21 which provide support for covers 31 and inner pots 41 whenand if all of the electrode assemblies 24 are removed from the furnaceat one time. However, electrode assemblies 24 may be removed singly orotherwise, as desired. While each cement block 22 contains but oneelectrode in the embodiment shown in this invention, there might, ofcourse, be as many electrodes in each block as desired.

Cable 42 is shown in Figure 4 attached to copper extension 28 and isconnected to a power source which may be on a sub-floor level forconvenience and safety. Mounting 35 is placed on each cover 31 toprovide for an attachment for cover raising means (not shown). It isseen, then, by removing the hinge pins and top 31 that one or moreelectrode assemblies 24 may be removed for repair or replacement withoutdisturbing the other components of this completely enclosed furnace andwithout any need for special sealing procedures after replacement.

In Figure 5 is shown an electrode removed from cement blocks 22, but theoutline of a block is shown in phantom as it would appear in a completedelectrode assembly. Transverse rods 43 are xed to the upper and lowerportions of bars 27, thereby providing a rigid anchor which tends tosecure the electrode in block 22. Adjustments and repeated removals ofthe electrode assembly from the furnace will not loosen the electrode inthe block.

Looking at Figure 6 is seen furnace housing 46 having a monolithicrefractory casting 47 placed therein. Located in the casting areelectrodes 48 through 51 having `cable attachments 52 through 55,connected to their yupper ends respectively. Looking at Figure 7 is.seen Aa `cross section of housing 46 comprising a refractory ceramicpot 56, metallic container 57, a non-conductive refractory separator 58,and a second metallic container 59. Also shown are stubs 60 welded orotherwise attached to `electrode 48, stubs 61 attached to electrode 49,.and stubs 62 and `63 attached respectively to electrodes 50, 51.AStu'bs 60, 61 are shown in elevation while stubs 62, 63 are shown incross section. About .each electrode is .seen a wrapping 64, which willdecompose with heat providing roomrfor expansion and contraction of theelectrodes in the refractory block. In Figure 8 is seen `a section takenat 8-8 of Figure 7 showing stubs 63 and electrode 51. As mentioned, thestubs may be recessed slightly in monolithic refractory 47 to preventcontact with the work (Figure 12). In this embodiment, electrodes 48through 51 are situated in a single refractory casting and therefore maybe lifted from the furnace together but they, of course, may be inseparate castings or a pair in a casting or otherwise arranged. In thisembodiment, electrodes 48, 50` are of one polarity while electrodes 49vand 51 are of another. There will be Acurrent ow between stubs ofdifferent polarity along the length of the electrodes resulting in auniform temperature bath. The stubs may be of the size, placement, orconfiguration to obtain desired resistances and temperature patterns'.

The cable attachments 52 through 55 are secured to cables, not shown,vafter the casting has been placed in the furnace. Power is appliedvbetween the .electrodes causing current flow between the stubs of`opposite polarity. This will bring the salt bath up to temperature andmaintain this temperature uniformly throughout while the power isapplied. The length of the electrode and the temperature at which theymay be used are increased due to the multiple supports supplied eachelectrode by its respective stub Vbeing formed in the refractorymaterial. Each stub may rest on the refractory castings supporting theelectrode Weight above it. 'I'he stubs may be wrapped in a materialwhich will decompose upon high temperatures so that clearance isprovided for the expansion of the electrode during the high temperature.It is also seen that the electrodes are largely protected from the saltbath and that the current flow takes place between the stubs rather thanthe electrodes. This preserves the electrodes by preventing localizedworn spots which would require their replacement.

Periodically casting 47 may be removed from the furnace and the stubsinspected. If any defective stubs are noticed they may be removed andreplaced and the casting re-inserted into the furnace. The stubs may bereplaced without disturbing the casting thereby saving time andresulting in further savings in time and cost. It may also be seen thatin this invention, unused bath portions, such as that portion whichusually surrounds the electrodes, is Ykept to a minimum therebyconserving the power ordinarily used to heat this unused portion. Inother words, especially in the furnace in Figures 6 8, practically allof the bath is available for work.

In Figure 9 is seen an embodiment where an electrode is supported at itsupper portion in a refractory casting while its lower portion is exposedto the salt bath. The pins attached to the electrode are used in thisembodiment only to provide spaced supports for the electrode in theCasting so that at high temperatures the weight of the electrode -willnot cause distortion of its upper portion. Furnace housing 46 housesyand supports electrodes 67, cas-ting 68 and supporting pins 69.Supporting pins 69 may be attached to electrode 67 by welding or byinsertion through holes preformed in electrode 67 or by other means.Refractory material is then cast about the electrode yand pins to formthe structure shown in Figure 9. Before casting, each pin may beenclosed with a material which will decompose at high temperature sothat a void is provided about each pin which will allow for expansionand contraction ofe1ectrodes67 incasting 68. Casting 68 may be securedto the `wall of Ifurnace 46 or may rest lagainst the wall of the furnaceto yfurnish the support tothe electrode to prevent undesirabledeformation. The portions of electrode 67 above castings 68 aresufficiently cool to prevent deformation and the vportions below thecastings are sutliciently short to .prevent any stretching if thecasting -is xed to the furnace wall or bending if the casting is `notfixed to the furnace wall.

Shown in Figure l1 is the-casting 68 which has only-a side wall`extending to the furnace bottom to Support the electrode castingcombination. A clearance between electrode 67 and the furnace bottomallows for electrode e'xpansion. Electrical conduction betweenelectrodes is .facilitated by placing the uncovered sides of a p'air ofelectrodes facing toward one another.

An enlarged section taken at 10-10 of Figure '9 is shown in Figure l0.Pins 69 are shown-inserted through the electrode 67 which is embedded incasting 68. The clearance or void between pins 69 and casting '68 canmore easily be seen and it is this clearance which allows for expansionand contraction of electrode 67 in casting 68 as the temperature risesand falls.

While particular preferred Vembodiments have been disclosed anddescribed above in detail, it Will be understood that numerousmodifications may be resorted to without departing from the scope ofthis invention las dened in the following claims.

I claim:

l. An electrode bath furnace 4comprising furnace electrodes, saidelectrodes each having a hot leg portion and a cold leg portion,supporting means projecting from said ot leg portion, `refractory means,said hot and cold leg portions at least partially embedded in saidrefractory means to provide an enclosable furnace and with said hot legportions at least partially supported by said means projectingtherefrom, a second bath heavier than said electrode bath disposed alongthe bottom of said furnace for receiving and suspending furnace wasteproducts thereby facilitating the removal thereof.

2. The furnace of claim l with said projecting means having end portionsexposed to the furnace bath, said hot leg portions being substantiallyenclosed by said reffractory means, and said hot and cold leg portionsbeing embedded in removable refractory segments.

3. The `furnace of claim 1 with said supporting means comprisinglaterally extending pins spaced lengthwise along said hot leg portions,said hot leg portion partially embedded in said refractory means so thata portion is exposed to the furnace bath for electrical connectiontherewith.

4. The furnace of claim 1 with said refractory means comprisingindividual refractory segments with a predeterm-ined number ofelectrodes embedded in each segment, said segments alignable along afurnace Iwall to form a substantially continuous enclosure.

5. A bath furnace electrode assembly comprising a plurality ofelectrodes, electrode pins, refractory castings, said pins beingattached to each electrode along a portion of the electrode, saidportion being embedded in a casting so that at least one of said pins issupported by said casting and in turn supports said electrode with aportion of said electrodes exposed so that electrical conduction maytake place in the furnace bath between said exposed portions.

6. An electrode heated salt bath furnace comprising a furnace enclosurehaving walls and a furnace bottom, electrodes, said electrodes having aportion embedded in refractory blocks, said blocks being aligned alongthe top of one of said walls, each of said blocks abutting a face of anadjacent block, said blocks forming a continuous Wall portion, a coverbeing located between the blocks on said one wall and the opposite wall,so that the furnace bath is completely covered keeping radiation lossesto a minimum.

7. An electrode heated salt bath furnace comprising a furnace enclosurehaving walls `and a furnace bottom, electrodes, said electrodes having aportion embedded in refractory blocks, said blocks being aligned alongthe top of one of said walls, each of said blocks abutting a face of anadjacent block, said blocks forming `a continuous wall portion, saidelectrodes comprising vertical depending members, horizontally outwardlyextending members, the inner portion `of each of said horizontal membersbeing connected to the upper portion of one of said vertical members,said upper and inner portions being embedded in said block so that thevertical portions depend downwardly from said block and the horizontalportions extend outwardly from said block, said blocks beingpositionedalong said wall so that said vertical portions are located interiorly ofsaid furnace and said horizontal portions extend outwardly of saidfurnace for connection to a power source.

8. The furnace `of claim 7 having `a top plate, said plate being placedover said blocks, a furnace cover, said cover being hinged to saidplate, said cover contacting said plate and said furnace walls so thatwhen said cover is in a closed position, a completely covered furnaceenclosure is provided keeping heating losses to a minimum, each of saidblocks being independently removable from said furnace withoutdisturbing said cover or said furnace walls.

9. The furnace of claim 8 where said inner horizontal portions of saidelectrodes have a plurality of transverse anchoring rods xed thereto sothat movement or looseness between said refractory material and saidhorizontal members is resisted.

10. A bath furnace electrode assembly comprising electrode means,supporting means, refractory means, said supporting means being attachedto said electrode means and tangible with said refractory means so thatat least a portion of said electrode means is supported by saidsupporting means to prevent electrode deformation, said supporting meanscomprising a plurality of lateral projections from said electrode means,said projections each having -a portion contacting said refractory meansso that projections which are in contact with and supported by saidrefractory means will in turn support the electrode means.

11. A bath furnace electrode assembly comprising electrode means,conduction means, refractory means, said electrode means being combinedwith said conduction means and this combination being embedded in saidrefractory means so that said conduction means has an exposed surfacefor electrical conduction and said electrode means is substantiallyisolated from 'said bath by said refractory means, said conduction meanscomprising a plurality of lateral projections from said electrode means,said projections each having an exposed surface and each projectionsupporting said electrode means in said refractory means, a clearancebetween each of said projections and -said refractory means to allow for`any difference in co-eicients of expansion between said electrode meansand said refractory means.

References Cited in the file of this patent UNITED STATES PATENTS1,376,615 Jacobs Apr. 5, 1921 2,234,476 Jessop Mar. 11, 1941 2,508,004Adam May 16, 1950 2,512,206 Holden et `al June 20, 1950 2,701,269 HoldenFeb. 1, 1955 2,826,623 Rousseau Mar. 11, 1958 FOREIGN PATENTS 529,891Great Britain Nov. 29, 1940

